Tribology of Carbide Derived Carbon Coatings Grown on Tungsten Carbide

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Tribology of Carbide Derived Carbon Coatings
Grown on Tungsten Carbide

• M. Tlustochowicz1, M. McNallan1, A. Erdemir2, S.
  Sudarshan3, and R. Radhakrishnan3
• University of Illinois, Chicago, IL
• Argonne National Laboratory, Argonne, IL
• Materials Modification, Inc., Fairfax, VA

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Etching in Halogens
Schematic showing how our CDC process differs
from other coating techniques, such as chemical
vapor deposition (CVD) and physical vapor
deposition (PVD), that are currently used to
produce carbon coatings.
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Properties of Carbide Derived Carbon

• Structure resembling
• partially graphite and
• partially diamond
• Diamond structures
• are found only close
• to the interface graphite and carbon onions
  are more common further away
• Nanoporous structure
• Residual chlorine present

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Challenges Posed by Conventional Microcrystalline
Tungsten Carbide (WC) Cermets

• Most commercial WC products are cermets
  containing typically 6 Co or Ni as binder
• Chlorination causes selective attack of the metal
  binding phase before carbide is etched
• Samples may experience significant weight loss or
  complete disintegration

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Nanocrystalline WC a Novel Material

• When the nc-WC is densified with minimal or no
  binder, appropriate selection of CDC processing
  conditions can produce coatings with tribological
  characteristics comparable to those of CDC on
  SiC.
• Nanoindentation results

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Typical Microcrystalline Cermet-WC Tribological
Results
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Nanocrystalline WC Tribological Results
After Treatment at 900 C
Friction coefficient versus time in pin-on-disk
test on nanocrystalline WC before and after
chlorination treatment at 900 C.
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Silicon Carbide Tribological Results
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Conclusions

• Carbide derived carbon (CDC) can be produced on
  nanocrystalline tungsten carbide by selective
  reaction of tungsten with chlorine
• When created in appropriate processing
  conditions, CDC significantly lowers the friction
  coefficient of WC
• CDC synthesized from nanocrystalline WC has
  similar tribological properties to these of CDC
  grown on SiC